Data transmission device for random access network, with improved collision resolution, and corresponding method

ABSTRACT

A data processing station wherein a network interface monitors the transmission channel and generates event signals, e.g. &#34;transmission start&#34; &#34;collision detected&#34; and &#34;channel back to vacant condition&#34;. If a collision occurs in local transmission, transmission is maintained with a collision indication for at least one period before being cut off. An observation register receives the event signals and responds by generating a channel observation signal which may be &#34;transmission OK&#34; &#34;collision slot&#34; and &#34;vacant slot&#34;. When transmission of a fresh data packet is requested, a first transmission may or may not be attempted (normal mode) depending on the condition of the observation register. If the attempt is unsuccessful (transmission refused or collision), a suitably reset mechanism for incrementing/decrementing a common integer determines the right to transmit, so that the response to a request for the transmission of a fresh data packet is made regardless of the channel&#39;s operating record, upstream from the last normal mode to be executed.

The invention concerns computer networks which allow the exchange ofinformation or "data" between different terminals.

Such a network conventionally comprises a transmission medium, generallyan electrical or fiber optic cable. Stations or terminals are connectedat various places on this cable, this connection being made through a"network interface".

It is essential for the terminals to understand each other, despitetheir multiplicity. In some computer networks, a rule (multiplexing,token) is determined for this purpose, in accordance with which no morethan one of the terminals may transmit over the communication medium ata given moment. Another technique permits "random access" to thenetwork, that is to say several terminals may transmit at the same time.One consequence of this multiple access is that "collisions" may occur,and it will then be necessary to resolve them.

The ETHERNET (registered trade mark) network, governed by the standardknown as IEEE 802.3, is of the random access type. The networkmanagement protocol is of the multiple access carrier sensing type withcollision detection, or CSMA/CD (Carrier Sense Multiple Access withCollision Detection).

One of the essential features of such a network is its ability to effecta "collision resolution" rapidly. This is because, when a transmissionhas given rise to a collision, it is necessary to recommencetransmission. This has the direct effect of increasing the instantaneousneed for transmission. As a result, if a multiple access channel isoperating with very high traffic, the collision resolution may takecorrespondingly longer, and consequently the waiting time for asuccessful transmission correspondingly more protracted.

The Applicant has moreover observed that at least two types of datatraffic can be distinguished:

a) data coming from sensors in real time, for example voice (telephony)or video (image);

b) exchanges of files or knowledge tables coming from bulk storage,which are pure data packets.

The Applicant has also observed that the constraints which are appliedto the exchange of these different types of data are fairly divergent.

Data coming from sensors in real time are generally fairly heavilyredundant. As a result it is possible to accept a significant loss ratefor these data packets without appreciable degradation of the quality ofthe data conveyed: it is known for example that voice telephony data,which are highly redundant, may be cut to a great extent without loss ofintelligibility. On the other hand, telephony data packets must becarried within strict time periods.

In contradistinction to this, exchanges of file data for example aremuch less sensitive to transmission times. On the other hand, they arenot able to sustain any level of data loss and are very demanding interms of passband. In addition, they require acknowledgement ofreception and flow monitoring protocols, which is not the case withvoice data packets for example.

This poses different problems, which the invention is aimed at helpingto resolve.

A first aim of the invention is to provide a better collision resolutiontechnique, which increases the efficacy of a multiple access channel.

The second aim of the invention is to allow the use and implementationof priority classes in the operation of this collision resolutiontechnique.

In order to form a computer network from a transmission medium orchannel, a device is associated with each data processing terminal,comprising:

a network interface, capable of the transmission/reception of messagesover the channel, with monitoring of the channel in order to establishevent signals, which selectively represent the detection of the start ofa transmission on the channel, the detection of any new collision, andthe detection of the return of the channel to the vacant state, and

a transmission/reception management device, for controlling the networkinterface in accordance with the event signals.

Means are provided, in general in the network interface, to ensure that,in the event of a collision, transmission is maintained (with indicationof collision) for a sufficient length of time for all the stationsconcerned (within range of the stations which are the cause of thecollision) to have detected this collision, after which all transmissionis interrupted. As a result a "collision slot" is defined.

According to a first aspect of the invention, the device comprises achannel observation register which receives any event signal and inresponse establishes a channel observation signal, amongst apredetermined set of possibilities, this set comprising transmission(emission or reception), "collision slot", or "vacant slot", thecollision time slot being made subject to a first minimum period (C),and the vacant slot existing only when the vacant channel state haslasted for a second minium period (B) at least equal to the maximumoutward and return propagation time for a signal on the channel and lessthan the first minimum period.

Consideration is now given to the time where the management device has anew packet to transmit, that is to say it receives a request to transmita data packet. It then awaits a predetermined number (>=1) ofrefreshings of the state of the observation register ("refreshing" meanschange of state or reconfirmation of the same state). A firsttransmission attempt may or may not be enabled, depending on theobserved sequence of change of state of the observation register."Failure" means the cases where the attempt at transmission is notenabled or those where it results in a collision. In the event offailure, the management device reacts by initializing a current integer(E), to a value between a first (0) and a second (M-1) limit integer,inclusive. It then causes the current integer (E) to vary in accordancewith a predetermined law, which is a function of the observation signal,or of sequences of values of this observation signal. It is preferablyensured that this sequence of observations does not go beyond the lastattempt at transmission or the last failure indexed.

The predetermined law is preferably chosen as follows: it tends to movethe current integer away from the first limit integer (0) if there is anabundance of collision slots; it tends to move it closer to it if thereis an abundance of vacant slots. The word "abundance" here refers to thefact that it is possible to use any absolute or relative representation(average, for example) of the number of collision slots, or vacantslots, obtained over the interval of time in question.

When the current integer (E) reaches the first limit integer (0), thedevice carries out a further observation of the channel in order toenable, or otherwise, a further attempt. In the event of failure, thedevice repeats the mechanism described above.

A person skilled in the art will understand that this collisionresolution technique requires continuous observation of the channel onlyduring two attempts to transmit any one packet. In other words, it doesnot require the maintenance at all times of a history, even partial, ofthe channel, upstream of the last attempt to transmit the packetconcerned. This denotes the originality of the novel technique comparedwith the Ethernet collision resolution method (Binary ExponentialBack-off) and the one described in French patent No 84 16 957, in thename of the Applicant, published under the No 2 597 686. This featureconfers significant properties of robustness and efficacy on thetechnique proposed.

The initial value of the chosen integer (E) is preferably substantiallyrandom. It may be supplied by a pseudo-random generator operating on aninteger of at least 10 bits, modulated by at least one integer of nomore than 10 bits, specific to the terminal concerned, the result beingreferred to the interval of the limits of the said chosen integer (E).

According to a variant of the invention, the current integer is alsotaken closer to the first limit integer when there is a transmissionwithout collision.

The invention may also be presented in the form of a collisionresolution method in a data transmission network of the multiple accesstype, the said method being open to the same variants as the devicedescribed above.

According to another characteristic of the invention, priority data areprovided, and also a comparison device based on data derived frompseudo-random quantities in order to favor the transmission of data ofhigher priority in the above-mentioned collision resolution technique.

Other characteristics and advantages of the invention will emerge froman examination of the following detailed description and accompanyingdrawings, in which:

FIG. 1 is a highly simplified diagram of a computer network in which thetransmission medium is a cable;

FIG. 2 is a partially detailed diagram of the network interface of aterminal;

FIG. 3 is a state diagram useful for the implementation of theinvention;

FIG. 4 is a skeleton flow diagram of the transmission monitoring andcollision resolution mechanisms used according to the invention;

FIG. 5 is a more detailed flow diagram of the transmission monitoringand collision resolution mechanisms used according to the invention;

FIG. 6 is a flow diagram illustrating the implementation of prioritymonitoring for the messages according to the invention; and

FIG. 7 is a flow diagram illustrating the maintenance of functions p_(i)(t) useful to the implementation of the priority monitoring.

The accompanying drawings are, essentially, of a definite nature. Theyconsequently form an integral part of the description and can not onlyserve to supplement it but also contribute to the definition of theinvention where appropriate.

In addition, the Applicant is on this date filing another patentapplication entitled "Data transmission installation of the radionetwork type, and corresponding method". Because of the technicalrelationships with the present Application, the description and thedrawings of this other Application can also be incorporated into thepresent description.

In FIG. 1, a transmission medium MT is connected to network interfacesIa to Ic, respectively connected to terminals Pa to Pc. This is theconventional structure of a data transmission computer network, to whichthe CSMA/CD protocol already mentioned can be applied, in accordancewith IEEE 802.3.

Experts are aware that the models defining such interfaces are specified"in layers" (ISO standard), to each of which a precise function isassigned. This partitioning into functional layers makes it possible toensure the compatibility of components of the network from differentsources, when they are interconnected. Reference will be made below tothis concept of layer. Moreover, distinction will be made between theprotocol layers proper and the upper layers of the protocol.

Terminals such as Pa are data processing terminals (the word processingis used here in the most elementary sense, since this processing may bevery simple). All processing carried out in the terminal is outside thedata transmission proper. However, in the terminal there may be specificoperations taking specific account of the nature of and certainconditions applicable to data transmission. These are the upper layersof the protocol.

The layers of the protocol itself will on the other hand govern thetransmission of data in its basic state, in a way which makes itpossible to ensure its security.

Each network interface I has a circuit RE for immediate connection tothe network. These components I and RE are separate in FIG. 2.

The unit RE supplies for example three detection signals, namely:

ECOLL: a collision has just taken place on the channel;

E/R, true if outward transmission is taking place, false duringreception;

ED0, which means, during reception, that no data has been received.

The signal ED0 is stored at T14 in order to give CD0, which remains trueas long as no data is received. The signal E/R is complemented by T11,in order to give REC, true during reception. REC is applied, togetherwith CD0 complemented by T15, to an AND function at T12, the output ofwhich therefore indicates the effective receipt of data. Finally, an ORfunction at T13 supplies the signal ETRA which represents change fromthe vacant channel state to a start of transmission (outwardtransmission or reception), and is stored at T16 in order to give thetransmission state CTRA.

Any collision detection ECOLL is stored at T10 in order to give CCOLL,repetitively. It is known that any transmission subject to collision canbe prolonged so that it lasts for a minimum time C, at least equal tothe maximum outward and return propagation time for a signal over thechannel MT, increased by the time required to detect a collision (inall, the minimum time necessary for a collision to be detected by allthe terminals connected to the channel MT; it is referred to here as the"collision slot").

The signals ED0 and CD0 represent the return of the channel MT to thevacant state, either at the end of a successful transmission or at theend of a transmission subject to collision.

In other words, the detector RE, which can also be referred to as a"tracer", makes it possible to establish the following information,preferably in the form of pulses or time and state transitions:

changing from the vacant channel state to a start of transmission(outward transmission or reception),

detection of a collision, during a transmission phase,

end of transmission with success (return to the vacant state),

end of transmission with collision (return to vacant state).

From there, the present invention provides for the definition ofobservations, which may be recorded in an observation register RO (FIG.2), complying with the state diagram in FIG. 3. Observation register ROprovides observation signals to network interface I viatransmission/reception management device DG. Network interface I alsoincludes pseudo-random generator GPA.

The concept of "vacant slot" should first of all be defined.

The "vacant slot" is an interval of time, the duration of which isdetermined in advance, and during which the transmission channel isvacant, that is to say it is not carrying any message. The minimumduration of a vacant slot is greater than the propagation time of asignal from end to end over the entire channel.

In other words, the vacant slot is the interval of time required for anobserver of the channel to be assured that no terminal has commencedtransmitting, having regard to the effect of the propagation times.

According to the present invention, the respective mean durations of thecollision slot and vacant slot are termed C and D. These durations aredetermined according to the structure of the transmission channel used.In the case of a radio network, as described in the parallel patentapplication mentioned above, the duration C must in principle be chosenso as to be fairly long, because of the coding techniques, withinterlacing, used for error detection. This is because it is thennecessary to have received a substantial quantity of information beforedecoding in order to be able to obtain the first decoded bit.

In FIG. 3, it is assumed that the starting point is a vacant slot (30)representing the observation OD0. On each occasion that a time B haselapsed, the vacant slot observation is renewed (31).

Each start of transmission (32) will bring about a change to theobservation OTRA at 33. This observation is renewable (34) if in themeantime there is a change to the vacant channel event for a time lessthan B.

Return to the vacant state will bring about a return to the observationOD0 at 30, but only at the end of the time B (arrow 39).

In the event of collision (35), we go to the observation OCOLL at 36.This observation is renewable (37) on each occasion that a time C haselapsed. There too, return to the vacant state will bring about a returnto the observation OD0 at 30, but only at the end of the time B (arrow38).

Reference is now made to FIG. 4. This illustrates a collision resolutionmechanism which can be produced by means of the management deviceincorporated in the unit I in FIG. 2.

The input 400 in FIG. 4 represents a situation in which a data packet isto be transmitted.

The step 401 designates the first channel observation phase, referred toas phase 1.

The step 402 determines, in accordance with the previous observationphase, whether an attempt may be made to transmit the packet. Forexample, the end of the current slot, and therefore the refreshing ofthe observation register, may be awaited; transmission is enabled onlyif the observation validated as the end of the slot is "vacant" or"transmission". More generally, the steps 401 and 402 may be based onany predetermined criterion involving a sequence of observations ofdeterminable length.

If yes, the step 403 demands the transmission of the packet. The test404 determines whether or not there is a collision (observation OCOLL)on this transmission. It is known that, when there is a collision, thenetwork interface provides for the continuation of the transmissionuntil the end of the minimum duration C of a collision slot.

In the absence of a collision, the transmission is successful, the datapacket is validated for the transmission, and this is the end of themechanism.

In the event of failure, we go to a second part of the mechanism, whichbegins at step 405 and concerns the collision resolution proper.

This step 405 consists of the selection of an integer E meetingpredetermined conditions, but preferably defined in a random manner. Ina particular embodiment, account is also taken of an integer specific tothe terminal, optionally a clock integer, that is to say one related totime.

The integer E lies between two limit integers, which are here denoted 0and M-1 (where M is at least 2).

The step 406 determines whether the current value of E is zero, in whichcase we go back to step 402 after a new phase of observation of thechannel 430, referred to as phase 2.

This phase 2, which may be the same as phase 1, delivers or does notdeliver a transmission attempt authorization.

If not, the step 410 consists of collecting the current observation ofthe channel, for example by reading the register RO. And the step 420consists of updating the integer E as a function of its previous valueand the observation or observations. That is to say the updating may beeffected either as a function of the last observation or of the seriesor sequence of last observations. After this updating, we return to step406.

In other words, the current integer (E) is updated by causing it to varyaccording to a predetermined law h(o,E), which is a function of theobservation signal o (or series of values of this observation signal)and of the previous value E.

It is a requirement for this law to tend to move the current integeraway from the first limit integer (0), in the event of an abundance ofcollision slots; it will tend to move it closer to it in the event of anabundance of vacant slots.

When the current integer (E) reaches the first limit integer (0), atransmission attempt will once again be enabled or otherwise (step 402),after a phase of observation of the channel (step 430).

A few examples of specific laws will be given below, before describing aparticular embodiment.

In general, observation is taken to mean one of the following threepossibilities: "vacant slot", "collision slot" and "transmission OK"(that is to say a period of transmission without any indication ofcollision). The variation laws for the current integer (E) may be:

h("collision",E)=E+M-1;

h("vacant slot",E)=E-1;

h("transmission OK",E)=E (or E-1, as a variant).

And for the observation phases for the purpose of transmissionauthorization:

phase 1 and 2: "authorization to transmit at the next end of slot"(refreshing of the observation register).

For phase 1, the following variant can be accepted:

phase 1: "await the next end of slot, and authorization to transmitexcept if the slot which is ending is a collision slot".

There are embodiments which are a little more sophisticated, using moreextensive observations. For example, M=2 gives the following modifiedprotocol:

Phase 2: "await the next end of slot, and authorization to transmitexcept if there is a series of vacant slots following on from acollision slot and the last failure goes back more than one vacantslot";

h("series of vacant slots after collision",E)=E, (if E>1), otherwise h'"vacant slot",E)=E-1 (that is to say when the last non-vacant slot isnot a collision slot).

This version may have better performance than the basic versions.Nevertheless, this modified protocol may pose a problem if the networkdoes not have very high reliability.

A particular embodiment will now be described with reference to FIG. 5(in which the steps correspond in general to those in FIG. 4, increasedby 100). At step 501, the authorization to transmit is based simply onwhether or not a collision is detected before the channel goes to thevacant state for the first time. The step 503 consists of a transmissionas soon as the channel is vacant. If E=0 at step 506, there will be adirect return to there (no physical step corresponding to 430, FIG. 4,the phase 2 condition being vacancy of the channel). Steps 512 to 526are a breakdown of step 420 in FIG. 4.

To summarise this particular embodiment:

what is referred to as "observation" or "o" is one of the followingthree possibilities: "vacant slot", "collision slot" and "transmissionOK",

this set is considered as follows. There is "transmission OK" as long asthere has not been a collision event (in fact, "collision slot") and thevacant channel state has not lasted sufficiently long (duration B) toconstitute a "vacant slot" There is a change to "vacant slot" only whenthe vacant channel event has lasted for duration B. When there has beena change to "collision slot", this lasts at least for the time C.

The predetermined law h(o,E) is then:

h("collision",E)=E+M-1

h("vacant",E)=max(E-1; 0)

where MAX takes the highest of its 2 arguments and, depending on thevariant chosen,

either h("transmission",E)=E

or h("transmission",E)=E-1

This can be referred to as "stacked collision resolution protocol".

It was stated above that the integer E lies between two limit integers,which are in this case denoted 0 and M-1. Mention has also been made ofincrementing and decrementing. Naturally, all these definitions arerelative, in that all the quantities referred to as integers may asdesired be multiplied or divided by the same factor, whilst preservingthe functioning of the invention. Likewise, the role of the two limitscan be transposed, as well as the incrementing and decrementingoperations.

In addition it is desirable, but not absolutely essential, for the limitinteger M-1 to be equal to the integer part of the ratio C/B between theduration of the collision slot and the duration of the vacant slot.

A means useful to the implementation of this mechanism is apseudo-random generator, which will supply, as a function of time, asignal representing a random integer which is denoted g(t).

A fairly general example of a pseudo-random generator consists of usinga congruent generator of integers, capable of supplying numbers of Dbits in a sequence of random appearance over a considerable time. D ispreferably around 10. The numbers thus presented follow each other at achosen frequency, with which a period T_(A) will be associated.

The number g(t) is for example a number between 0 and 1, which iswritten in binary as the D bits in question.

In a known manner, the generation of pseudo-random numbers of this typemay be based on an operator using two specific integers p and q, andsupplying a calculated integer x(t) by means of the operation

    x(t)=p*x(t-T.sub.A)+q (modulo 2.sup.D)

The expression (modulo 2^(D)) means that the result of the operation isreferred to the remainder of its integer division by 2^(D), as is knownby persons skilled in the art.

Persons skilled in the art also know that it is possible to choose thenumbers p and q so that the series of numbers x(t) describe all thenumbers of D bits possible, in a quasi-disordered fashion, with alooping period of 2^(D) *T_(A).

Using such an operator, the number g(t) is obtained by the operation

    g(t)≡x(t)+i+k (modulo 2.sup.D)

In this relationship, i is an integer specific to the terminal, forexample the serial number of a component, or the address of the terminalin the network; k is the integer value of a local clock counter at thetime in question.

It may happen that the number i has a length exceeding D bits. In thiscase, the number chosen is divided into different packets with sizes ofD bits and the subpackets thus obtained are used successively andperiodically in place of i.

It is also possible to carry out the updates of the number g(t) solelyat the moment when the mechanism is consulting and making use of thisnumber g(t), instead of keeping to a periodic re-updating of periodT_(A).

It is also possible that, at the time of each consultation, an operationother than updating could be carried out on the number g(t) (for exampleretaining only a limited number of bits), in order to maintain therandom appearance between two consultations separated by less than T_(A)units of time.

The question of the message transmission priorities will now beconsidered.

Monitoring times are defined with a periodicity T_(A).

Step 700 (FIG. 6) selects the packet awaiting transmission pd_(i) whichhas the highest priority i.

At step 702, a pseudo-random number will be selected, the current valueof which is denoted g(t) (this g(t) may be the same as for the collisionresolution).

At the same time, a series of quantities of probability p_(i) (t) ismaintained, equal in number to the number n of priority levels to bemanaged (i goes from 1 to n). This will be described in detail later.

It is clear that the transmission/reception manager can, duringtransmission, manage only a single packet at any one time. It is assumedthat other packets awaiting transmission may be stored in an upstreambuffer managed by the upper layers of the protocol. A necessarycondition is the fact that any packet to be transmitted must first bestored in the upstream buffer before being directed to thetransmission/reception manager as described below.

When the transmission/reception manager is vacant, for any packet storedin the upstream buffer--let its priority be i--a comparison (704) iscarried out (700) between the associated quantity p_(i) (t) and thenumber g(t) selected at step 702. The order of consultation of thepackets is left to choice, and the operation is repeated when all thepackets have been consulted. The packet PD_(i) is transmitted (706) tothe transmission/reception manager with a request to transmit only ifg(t)<=p_(i) (t) at 704. In this case the selection mechanism is madedormant until the transmission/reception manager becomes vacant again(that is to say when the previous packet PD_(i) has been validated fortransmission). Otherwise a time TA is waited and we go back to 700.

A so-called "preemption" variant consists of not waiting for thetransmission/reception manager to be vacant to carry out the selectionof a new packet in the upstream buffer. In this case, it is preferablefor the transfer to take place only if the priority of the new packetselected is higher than the priority of the packet which is alreadypresent in the transmission/reception manager. The latter packet willthen be returned to the upstream buffer.

A person skilled in the art will understand that the priority managementis meaningful only as from the time when the communication request issuch that the performance of the network may thereby be degraded. Therole of the priority management mechanism is to decide, in accordancewith the traffic constraints, on the transfer of such a packet from theupstream buffer to the collision management device, and thus to monitorand limit the total instantaneous traffic which actually has access tothe communication medium in accordance with competing priorities.

This may apply not only in order to give different priorities to voiceframes and data frames (files), but also for example to service frames,such as so-called ADF frames, useful to the radio network of theabove-mentioned parallel patent application.

Each quantity p_(i) (t) is maintained (FIG. 7) in accordance with the"observations" defined above, by means of another law or re-updatingfunction q_(i) (p_(i) (t), "o"), where "o" designates an observation orseries of observations. As before, even if it is identical to theprevious one, any observation (or series of observations) brings aboutan updating of p_(i) (t).

The law or function q() should tend to decrease p_(i) (t) in the eventof an abundance of collision slots; it will tend to increase it in theevent of an abundance of vacant slots.

In a particular embodiment, the "observations" or "o" are just one ofthe three possibilities mentioned above: "vacant slot", "collision slot"and "transmission OK".

It is also accepted that each quantity p_(i) (t) is suitablyinitialized, and that its initial value may moreover be 0.

The predetermined law q_(i) (p_(i) (t), "o") is then:

    q.sub.i (p.sub.i (t), "collision")=Max {m.sub.i ; a*p.sub.i (t)}

where MAX takes the higher of its two arguments,

    q.sub.i (p.sub.i (t), "vacant")=Min {M.sub.i ; b.sub.i *p.sub.i (t)}

where Min takes the lower of its two arguments, and, depending on thevariant chosen,

    q.sub.i (p.sub.i (t), "transmission")=p.sub.i (t)

or

    q.sub.i (p.sub.i (t), "transmission")=Min {M.sub.i ; b*p.sub.i (t)}

This variant is coupled to those of the collision resolution, definedabove.

It is necessary for a_(i), m_(i) and M_(i) to be strictly lower than 1,and b_(i) strictly higher than 1.

The coherence of the priority mechanism means that, wherever i>0,

    a.sub.i *(b.sub.i).sup.M- 1>a.sub.i-1 *(b.sub.i-1).sup.M- 1

Thus, in adjusting the parameters a and b according to the "degree ofconnection" M, account is taken of the product of a, and of b itselfraised to the power M-1.

If the stacked collision resolution protocol is used (the detailedembodiment defined above), it is necessary for all the products a_(i)*(b_(i))^(M-) 1 to be less than 1.

In fact, the closer this product is to unity, the less the quantity ofinstantaneous traffic undergoes any restriction and the more theperformance in critical utilization of the network is degraded.

We claim:
 1. A device for connecting a data processing terminal to atransmission channel in a computer network, comprising:a networkinterface capable of transmission/reception of messages over thetransmission channel and monitoring of the transmission channel in orderto establish event signals which represent a detection of the start of atransmission on the transmission channel, a detection of a newcollision, and a detection of a return of the transmission channel to avacant state, a transmission/reception management device for controllingthe network interface in accordance with the event signals, and a meansfor ensuring that, in the event of a collision, transmission ismaintained, with indication of the collision, for at least a firstminimum period, after which all transmission is interrupted, wherein themeans for ensuring includes a channel observation register whichreceives the event signals and in response establishes a channelobservation signal having a predetermined set of possible statesincluding transmission OK, "collision slot" and "vacant slot", thechannel observation register being refreshed at least upon a channelvacant event, and wherein the management device reacts to a request forthe transmission of a new data packet according to the channelobservation register by:a) being in a normal mode, the normal modeincluding awaiting the next refreshing of the channel observationregister, and effecting or not effecting a first transmission attempt inaccordance with a predetermined criterion applied to the state of thechannel observation register prior to said next refreshing, b) in theevent of failure,b1) initializing a current integer to a value between afirst and a second limit integer, inclusive, and b2) modifying thecurrent integer at each change of state of the channel observationregister, in accordance with a predetermined law which tends to move thecurrent integer away from the first limit integer if there is anabundance of collision slots, and to move the current integer closer tothe first limit integer if there is an abundance of vacant slots, andreturning to the normal mode only when the current integer has reachedthe first limit integer so that the reaction of the management device toa request for transmission of a new data packet is independent of thehistory of the channel prior to the last normal mode executed.
 2. Adevice according to claim 1, wherein the predetermined criterioncomprises the absence of a collision slot.
 3. A device according toclaim 1, wherein the transmission observation is confirmed, after astart of transmission event, when there is a channel vacant event notpreceded by a collision since the start of the transmission, in that thecollision time slot observation is confirmed at a channel vacant eventwhich follows the transmission with signalling of collision, and in thatthe vacant slot observation is confirmed when the channel vacant slothas lasted for a second minium period.
 4. A device according to claim 1,wherein the initial value of the chosen integer is substantially random.5. A device according to claim 1, wherein the current integer is alsomoved closer to the first limit integer when there is a transmissionwithout collision.
 6. A device according to claim 1, wherein the saidpredetermined law comprises:as long as the current integer is not equalto the first limit integer, incrementing the current integer by a firstchosen step if the channel observation register indicates a collisionslot, or decrementing the current integer by a second chosen step if thechannel observation register indicates a vacant slot, the ratio of thefirst step to the second step being substantially equal to thedifference between the two limit integers.
 7. A device according toclaim 1, wherein the transmission/reception management device does nottransmit if a collision state already exists when thetransmission/reception management device receives a request to transmit.8. A device according to claim 1, wherein the difference between the twolimit integers is substantially equal to an integer part of the ratio ofthe first period to the second period.
 9. A device according to claim 1,wherein the current integer is supplied by a pseudo-random generatorwhich modulates an integer of at least 10 bits by at least one integerof no more than 10 bits, specific to the data processing terminal.
 10. Adevice according to claim 9, wherein the current integer is supplied bya pseudo-random generator which modulates an integer of at least 10 bitsby at least one integer of no more than 10 bits, specific to the dataprocessing terminal, and by a clock integer.
 11. A device according toclaim 1, wherein the requests for the transmission of a new data packetare accompanied by priority information from a predetermined set ofpriority classes, and wherein the management device maintains, for eachpriority class, a quantity representing a level of occupation of thetransmission channel, such that a current request is taken into accountonly if the said quantity for the priority class corresponding to thecurrent request is in a predetermined relationship with a randomquantity.
 12. A device according to claim 11, wherein each quantityvaries in accordance with a predetermined law which is a function of thechannel observation signal, in order to increase the correspondingoccupation of the transmission channel in the case of a collision slot,and to decrease the corresponding occupation of the transmission channelin the case of a vacant slot.
 13. A device according to claim 12,wherein the quantity is also modified by the management device to reducethe corresponding occupation of the transmission channel when there is atransmission without collision.
 14. A device according to claim 11,wherein the quantities and the random quantity are standardized to unityby the management device such that, for a representative quantity, thepredetermined relationship is a comparison of the random quantity withthe representative quantity.
 15. A method for the resolution ofcollisions in a data transmission network of the random access typewhere each terminal is provided with a network interface suitable fortransmission/reception on a transmission channel, with monitoring of thechannel in order to establish event signals which selectively representdetection of a start of transmission, detection of a new collision, anddetection of a return of the channel to a vacant state,wherein, upon arequest to transmit a data packet, the data packet is transmitted assoon as the vacant state is obtained in the absence of a collision,thereby enabling transmission of a current data packet, and return to astate of awaiting a request to transmit another data packet, andwherein, when there is a collision, transmission is extended for a firstchosen period and then interrupted, wherein, in response to an eventsignal, a channel observation signal is established from amongst apredetermined set of possibilities comprising transmission (emission orreception), "collision slot" and "vacant slot" the collision slot beingmade subject to a first minimum period from a new collision detection,and the vacant slot existing only when the vacant state has lasted for asecond minimum period at least equal to a maximum outward and returnpropagation time for a signal on the transmission channel and less thanthe first minimum period, and wherein, when there is a collision, i) acurrent integer is initialized at a value between a first and a secondlimit integer, inclusive, ii) on a new observation, the current integeris varied in accordance with a predetermined law which is a function ofthe new observation, in order to move the current integer away from thefirst limit integer if there is an abundance of collision slots and tomove the current integer closer to the first limit integer if there isan abundance of vacant slots, iii) transmission being possible only whenthe current integer reaches the first limit integer.